1. Field of the Invention
The present invention relates to calibration for maintaining the image quality.
2. Description of the Related Art
The image quality of an image forming apparatus varies depending on its use environment and use condition. The image quality also varies depending on the type of printing medium to be used. It is therefore necessary to change the image conversion conditions and image forming conditions depending on the environment and use condition (Japanese Patent Laid-Open No. 07-261479). In some cases, image conversion conditions and image forming conditions need to be added in accordance with the type of printing medium to be used (Japanese Patent Laid-Open No. 08-287217).
The invention in Japanese Patent Laid-Open No. 07-261479 assumes the use of a specific type of printing medium (to be referred to as the first printing medium) for calibration each time. If the first printing medium runs out, no calibration can be performed. Even in the invention of Japanese Patent Laid-Open No. 08-287217, performing calibration for an added arbitrary type of printing medium (to be referred to as the second printing medium) requires that a printing medium of the same type prepared each time. This is because the calibration aims to maintain the tone characteristic for the added second printing medium. If calibration is performed using the second printing medium of a type different from the first printing medium, for example, the amount of applied toner may become insufficient or exceed a permissible range designed for the image formation apparatus. This means that the image quality cannot be maintained. It would be convenient for the operator if calibration for a desired printing medium can be performed using another type of printing medium. For example, the use of an OHT (Overhead Transparency) sheet is designated for calibration for maintaining the tone characteristic for the OHT sheet. However, making plain paper usable for calibration to maintain the tone characteristic for the OHT sheet brings about significant advantages to the operator.